The invention relates to disc arthroplasty (or partial disc replacement) and, more particularly, to a nucleus replacement that mimics a native annulus in shape and function for use in partial disc arthroplasty.
The gold standard for the lumbar and cervical disc degeneration is currently fusion of the diseased motion-segment. The outcomes of the various fusion techniques have generally been satisfactory. Elimination of motion at a joint naturally produces stiffness and this in turn leads to transfer of forces normally absorbed by the motion-segments to the adjacent joints. As a result of the increased forces to which the adjoining joints are subjected, accelerated wear and tear takes place, setting the scene for arthritis at those joints. These observations have lead, therefore, to a search for alternative surgical treatments that would alleviate pain and restore function while preserving motion. Recently, a number of artificial disc prostheses have come into clinical use both in the lumbar spine and the cervicle spine. The results of these procedures, on medium term follow-ups, have been equivalent to fusion. Most of the devices for total disc replacement are performed anteriorly (through the belly) for the lumbar spine and the cervicle spine. The surgical trauma for the lumbar disc replacement is significant, and the approach has been associated with serious complications.
The current minimally invasive partial disc replacement devices are at experimental stages in the USA, and most have significant design flaws, notably instability of the devices in the disc spaces, and reliance on the already compromised annulus fibrosus to contain the devices. Furthermore, implantation of the current devices requires further violation of the annulus to implant the devices.